D. W. Johnson—contributing editor
Effects of Frequency, Percolation, and Axisymmetric Microstructure on the Electrical Response of Hot-Pressed Alumina–Silicon Carbide Whisker Composites
Article first published online: 18 OCT 2010
© 2010 The American Ceramic Society
Journal of the American Ceramic Society
Volume 94, Issue 4, pages 1125–1132, April 2011
How to Cite
Bertram, B. D. and Gerhardt, R. A. (2011), Effects of Frequency, Percolation, and Axisymmetric Microstructure on the Electrical Response of Hot-Pressed Alumina–Silicon Carbide Whisker Composites. Journal of the American Ceramic Society, 94: 1125–1132. doi: 10.1111/j.1551-2916.2010.04156.x
This work was financially supported by NSF DMR-0604211.
- Issue published online: 31 MAR 2011
- Article first published online: 18 OCT 2010
- Manuscript No. 27583. Received February 18, 2010; approved September 3, 2010.
The electrical and dielectric properties of hot-pressed composites containing alumina and silicon carbide (SiC) whiskers were characterized over a wide frequency range (0.1 Hz–1.8 GHz). The results were correlated to the average distances between SiC inclusions which were measured by stereology as a function of orientation and composition. Percolation of the whiskers caused a drastic increase in the dc conductivity and the prominence of a dc-conductivity tail associated with a high-frequency Maxwell–Wagner interfacial polarization. In percolated samples, the tail obscured the dielectric loss peak and there was evidence for the fluctuation-induced tunneling mechanism of conduction. In nonpercolated samples, the loss peak was observed and the complex permittivity data were fit with a modified Maxwell–Wagner equation to account for a distribution of relaxation times. The frequency–dispersion magnitudes, fitting exponents, and central relaxation times were orientation-dependent. Also, a damped resonance was observed between 1.4 and 1.7 GHz. The influence of the results on the microwave-heating application is discussed.